I. Field of the Invention
The present invention relates to image processing. More particularly, the present invention relates to a novel and improved system and method for interframe video coding based upon motion compensated predictive discrete cosine transform coding techniques.
II. Description of the Related Art
In the field of transmission and reception of television signals, various improvements are being made to the NTSC (National Television Systems Committee) System. Developments in the field of television are commonly directed towards a high definition television (HDTV) system. In the early development of HDTV, system developers have merely applied the Nyquist sampling theorem and low-pass filter design with varying degrees of success. Modulation in these systems amounts to nothing more than a simple mapping of an analog quantity to a value of signal amplitude or frequency.
It has most recently been recognized that it is possible to achieve further improvements in HDTV systems by using digital techniques. Many of the early HDTV transmission proposals share common factors. These systems all involve digital processing of the video signal, which necessitates analog-to-digital (A/D) conversion of the video signal. An analog transmission format is then used thereby necessitating conversion of the digitally processed picture back to analog form for transmission.
The receiver/processor must then reverse the process in order to provide image display. The received analog signal is therefore digitized, stored, processed and reconstructed into a signal according to the interface format used between the receiver/processor and the HDTV display. Furthermore the signal is most likely converted back to analog form once more for display.
Many of the conversion operations mentioned above, however, may be avoided using a digital transmission format which transmits the processed picture, along with control, audio and authorization signals, using digital modulation techniques. The receiver may then be configured as a digital modem with digital outputs to the video processor function. Of course, the modem requires an A/D function as part of operation, but this implementation may only require a 4-bit resolution device rather than the 8-bit resolution device required by analog format receivers.
Digital transmission is superior to analog transmission in many ways. Digital transmissions provide efficient use of power which is particularly important to satellite transmission and military applications. Digital transmissions also provides a robustness of the communications link to impairments such as multipath and jamming. Furthermore digital transmission facilitates ease in signal encryption, necessary for many military and broadcast applications.
Digital transmission formats have been avoided in previous HDTV system proposals primarily because of the incorrect belief that they inherently require excessive bandwidth. Therefore in order to realize the benefits of digital transmission, it is necessary to substantially compress the HDTV signal. HDTV signal compression must therefore be achieved to a level that enables transmission at bandwidths comparable to that required by analog transmission formats. Such levels of signal compression coupled with digital transmission of the signal will enable a HDTV system to operate on less power with greater immunity to channel impairments.
Motion estimation/motion compensation techniques can be used to compress the amount of data required in the transmission of interframe coded motion video. Motion estimation/motion compensation processes exploit the high level of temporal redundancy in video data. This high level of temporal redundancy is a neccesary attribute of video data for the picture sequences to appear continuous. The process of estimating the motion of objects within a video sequence is known as motion estimation. The processing of images by compensating for the presence of motion in a scene or image is motion compensation. The combined processes of motion estimation and motion compensation produce a prediction of the current frame of data. The error in this prediction, known as the residual, can be further compressed and transmitted.
It is therefore an object of the present invention to provide a novel and improved method and system for compressing HDTV signals that will enable digital transmission at bandwidths comparable to that of analog transmission of conventional TV signals.